1. Field of the Invention
This invention is directed to the linkage systems of mechanical arms. It is particularly directed to a four bar linkage assembly. It provides such an assembly especially adapted for use in a dental unit flex arm.
2. State of the Art
Mechanical support arms utilizing four bar linkage assemblies are utilized in a variety of settings. Such arms are typically used to support loads at adjustable locations. In a dental operatory, for example, dental instruments and fixtures may be supported by a mechanical, or "flex," arm within reach of a dentist. The arm typically includes a brake mechanism for locking the load in a selected position. When the brake is released, the load-bearing end of the arm may be raised or lowered as desired. The load-bearing end typically supports a "head" fixture which maintains a selected "level" attitude with respect to vertical and horizontal reference planes. "Horizontal," in this context, refers to approximately parallel the surface of the earth.
In a typical arrangement, an elongated arm member is pivotally fastened at a first end to an end post. The end post may be fixed or movable, but in any case comprises an anchor for the mechanical arm. A second end of the arm is pivotally fastened to a support post, which comprises a connection mechanism for a positionable load. The pivot axis of the arm member at the end post is ordinarily horizontally disposed so that the load-bearing end can be moved up or down vertically. A mechanism may also be provided to permit the arm to pivot around a vertical axis at the end post. The pivot axis of the arm member at the support post is also typically approximately horizontally disposed. The head fixture is typically connected through a mechanism proving for pivoting around an approximately vertical axis at the support post.
U.S. Pat. No. 5,340,072, the disclosure of which is incorporated by reference as a part of this disclosure, illustrates a four bar linkage system of the type described. A rod is pivotally connected to both the end post and the support post. The rod and arm are pinned to the posts in generally parallel orientation. A tray is mounted to the support post to be rotatable about a vertical axis. The parallel linkage assembly comprised of the arm, the rod and the two posts functions to maintain the orientation of the support post relative to vertical as the arm is pivoted up and down at the end post. A spring is positioned about the rod, and reacts between the rod and the end post to counter the weight of the arm system. The spring thus prevents the load end of the arm from falling under its own weight when the brake is released. The resistance of the spring is adjustable, but with considerable inconvenience. The effective length of the rod is adjustable to compensate for sag of the arm resulting from wear or heavy loads.
Currently available dental operatory flex arms are mechanically complex, and are relatively costly to manufacture. They are difficult to disassemble in the field for maintenance. It is generally impractical for a clinician to effect adjustments of spring tension and leveling (at the support post). Disassembly is hazardous because of the lack of suitable means for relieving stored spring energy. There remains a need for an improved mechanical arm assembly for use in dental operatories and other environments.